1. Field of the Invention
The invention relates to a method for monitoring performance test stands having at least one load assembly which is coupled to a test subject, such as an internal combustion engine, vehicle drive, or drive train, comprising the ascertainment of multiple, possibly derived parameters which characterize the current state of the test stand, and their automated evaluation in regard to the stability of the operating state of the test stand, and a performance test stand having at least one load assembly which is coupled to a test subject, such as an internal combustion engine, vehicle drive, or drive train, also having a test stand controller, possibly a higher-order test stand automation, and an analysis unit for ascertaining multiple, possibly derived parameters which characterize the current state of the test stand, and their automated evaluation in regard to the stability of the operating state of the test stand.
A test stand configuration, comprising an internal combustion engine as the test subject, for example, which is coupled to a load assembly, is fundamentally oscillatory because of its mechanical construction, because it has at least one torsion-elastic section and/or one torsion-elastic element in each case. The load assembly may comprise one or more load machines, which may operate connected in series or in parallel via intermediate gears and/or cumulative gears. For example, a connection shaft—in particular in engine test stands—acts between the load assembly and the test subject as the torsion-elastic element, for example, also a half-axis on a drive train, to which the load assembly may be coupled directly. However, the torsion-elastic element may also be inside the test subject and/or the load assembly. A measuring flange also represents a torsion-elastic element in principle. The mechanical test stand configuration may therefore be simulated by a multi-mass spring damper system. Upon specific excitation, this construction may become unstable and trigger mechanical destruction of individual components and/or corrupt the measurements. In order to allow secure, automatic operation, possible instabilities are to be recognized early, so that countermeasures may be triggered by the automation system and/or control system of the test stand. However, in the event of manual operation by inexperienced test stand operators, it is also necessary to recognize occurring instabilities automatically to ensure the operational security.
The object of the present invention is therefore to allow reliable recognition of instabilities in performance test stands of greatly varying configurations in the typical control modes and reliable online monitoring of the stability of the control circuits on performance test stands in real time with CPU use which preserves resources as much as possible.
2. Summary of the Invention
To achieve this object, the method is characterized according to the invention in that every parameter is standardized, the standardized parameters are weighted and consolidated into a single index which is characteristic for the current state, and this index is provided for the display and/or as a control variable for the real-time test stand controller. Therefore, an easily interpretable variable for the system stability is already provided in manual operation, in that, for example, a defined stability index is provided, independently of the test stand configuration, between 0 for stable and 100 for unstable. After the test stand configuration and thus the system behavior are not precisely known and the computing possibilities are restricted, exclusively signal-supported methods are used for the monitoring. Therefore, existing measuring and control variables such as engine speed, torque, pedal value setting (corresponding to the gas pedal setting in the vehicle), or braking speed are preferably used as parameters. An optimum method use is generated for the particular standard control mode and/or test mode. Because of the standardization, a reliable and simple recognition on a uniform basis is ensured in every test stand configuration. This solution according to the invention may be applied for test modes subjects which are fundamentally arbitrary, for example, for an internal combustion engine, for vehicle drives of all types, including electric motors and/or hybrid drives, or for drivetrains.
It is preferably provided that the weighting of the standardized parameters is performed as a function of the operating mode of the test stand. The test mode and the control mode determine the operating mode.
A simple variant, which nonetheless results rapidly in good stability information, provides that the standard deviation is determined over a defined period of time for detected parameters of the test stand or their chronological derivative.
Furthermore, it is advantageously provided that detected parameters of the test stand may be restricted to defined frequency ranges.
According to an advantageous variant of the method, after the sampling and before the ascertainment of the particular parameter, downsampling is applied, the resulting sampling being adapted to the particular frequency range of interest.
According to a further advantageous variant, a frequency analysis may be applied to detected parameters of the test stand.
According to a further embodiment of the invention, it may be provided that an index about the performance implemented in the connection shaft is ascertained from detected parameters of the test stand.
Various variants are conceivable concerning the selection of the parameters used for the stability monitoring, so that, for example, in the idle mode and/or upon specification of a torque of the load assembly, a torque signal is recorded and a characteristic parameter is obtained from a frequency analysis.
On the other hand, it may also be provided that upon specification of a speed of the load assembly, a torque signal is recorded and a characteristic parameter is obtained by determining the standard deviation.
A variant is also possible in which, in the idle mode and/or upon specification of a torque of the load assembly, the speed of the test subject is recorded and a characteristic parameter is obtained by determining the standard deviation.
Furthermore, it may be provided that in idle or upon specification of a torque of the load assembly in stationary operating points, the speed of the load assembly is recorded and a characteristic parameter is obtained by determining the standard deviation.
Another variant provides that upon specification of a speed of the load assembly, a characteristic parameter is obtained from a frequency analysis of this speed.
In all stationary operating points, according to a further embodiment, the manipulated variables for the load assembly and/or the test subject may be monitored and a characteristic parameter is obtained by determining the standard deviation.
It is advantageously provided that to standardize the torque analysis result, a torque characteristic of the load assembly is used.
On the other hand, it may be provided that to standardize the speed analysis result of the load assembly, a speed characteristic of the load assembly is used.
Advantageously, a speed characteristic of the test subject is used to standardize the analysis result of the speed of the test subject.
In contrast, it is expedient if a characteristic of the load assembly is used to standardize the manipulated variable analysis result of the load assembly.
According to a further variant of the invention, it may be provided that the angular acceleration of the load assembly is ascertained and its standard deviation is obtained as the characteristic parameter.
It is advantageous if physical characteristics of the load assembly are used to standardize the standard deviation of the angular acceleration.
Furthermore, an embodiment of the method may be provided, according to which the performance implemented in the connection shaft is obtained as a characteristic parameter.
An advantageous embodiment provides that a characteristic of the load assembly is used to standardize the performance implemented in the connection shaft.
For all of the above-mentioned variants, it may be expedient if all characteristics of the test stand and/or the test subject required for the method are taken from the parameterization of the test stand in the test stand controller and/or the values predetermined in the test stand automation. Therefore, for every test stand configuration, the simple and reliable recognition of instabilities may be ensured automatically and without additional parameterization effort.
Furthermore, it is advantageously provided that the index of the test stand controller is provided and a predefined reaction is triggered automatically as a function of this index. Via the automatically configurable reaction of the higher-order automation system by corresponding actions, which are to be defined by the test stand operator, such as engine stop, cold-running or idle operation, to the stability index, the test stand system may be reliably protected from damage. The index may alternately be transmitted via an analog value such as voltage, current strength, frequency, or the like, or as a digital value. A direct connection of the unit ascertaining the index to the automation system or the test stand controller may also be provided, as well as optionally a bus system, to which both components are connected.
To solve the problems stated at the beginning, a performance test stand is characterized according to the invention in that in the test stand automation, preferably in the test stand controller, a module is implemented, in which each parameter is standardized according to a method according to one of the preceding paragraphs, the standardized parameters are weighted and consolidated into an index characteristic for the current state, which is available for the display and/or as a control variable for the real-time test stand controller. The cited module may be implemented as software or hardware, possibly also in analog technology.
A display is advantageously provided for the index.
The invention is explained in greater detail on the basis of preferred exemplary embodiments in the following description.